MPs are warning of a crisis as tens of thousands of illegal immigrants from Afghanistan and the Middle East are smuggled into Europe.

They spoke out after seeing squalid scenes in a detention centre on the Greek-Turkish border which has become the front line for migrants trying to reach London, Paris and Berlin.

Keith Vaz, chairman of the all-party home affairs select committee, said a "humanitarian crisis" was building up that would eventually risk becoming a flood of illegal migrants to Britain.

"The point we need to grasp is that our border is no longer at Calais," said Mr Vaz. "It is now at Greece and Turkey because that is where the traffickers are bringing people over. What we saw was a humanitarian crisis in the making, with inevitable consequences for Britain if the controls break down."

The MP, a former minister for Europe, led a delegation of committee members on a fact-finding trip. They visited a centre at Filakeio, two hours drive from Athens, one of 10 trying to handle migrants. "The first thing that hit us was the terrible stench and overcrowding," said Mr Vaz.

"People were crying out, 'freedom, freedom'. Although the conditions were dreadful, you cannot just blame the Greeks because they are simply overwhelmed. The whole EU should be worried because the destination of choice for these migrants is western Europe, including London."

The committee is investigating the implications of Turkey joining the EU, which could mean the EU border expanding even further to Iraq and Syria.